The present invention relates to a technique for manufacturing bump electrodes on electrode pads.
As a technique for manufacturing bump electrodes on electrode pads of a semiconductor chip or electrode pads of a circuit board, a technique for manufacturing bumps comprising forming bump electrodes by using a solder paste material in a semi-solid state formed by kneading solder particles and a flux is described, for example, in Japanese Patent Laid-Open No. 263448/1995 and Japanese Patent Laid-Open No. 330719/1996.
The technique for manufacturing bumps (A) described in Japanese Patent Laid-Open No. 263448/1995 is as follows:
Firstly, a screen mask comprising a glass material is fitted on (attached to) a flat plate. The screen mask has openings (through holes), in which a solder paste material for forming bump electrodes is filled. A solder paste material is then filled in the openings of the screen mask with a squeegee. The screen mask is then removed from the flat plate along with the solder paste material filled in the openings of the screen mask. The screen mask is then fitted on a semiconductor chip or a circuit board (hereinafter, a semiconductor chip and a circuit board are called in general a substrate) under the condition in that electrode pads of a semiconductor chip or electrode pads of a circuit board face the openings of the screen mask. A heat treatment is then conducted to melt the solder paste material filled in the openings of the screen mask, so as to form bump electrodes. According to the manner, bump electrodes are formed on the electrode pads of the substrate.
The technique for manufacturing bumps (B) described in Japanese Patent Laid-Open No. 330719/1996 is as follows:
Firstly, a screen mask comprising a stainless steel material is fitted on (attached to) a substrate. The fitting of the screen mask is conducted under the condition in that electrode pads of the substrate face openings (through holes) of the screen mask. A solder paste material is then filled in the openings of the screen mask with a squeegee. The screen mask is then removed from the substrate in such a manner that the solder paste material filled in the openings of the screen mask remains on the electrode pads of the substrate. A heat treatment is then conducted to melt the solder paste material on the electrode pads of the substrate, so as to form bump electrodes. According to the manner, bump electrodes are formed on the electrode pads of the substrate.
Because the composition of the solder paste material can be freely selected in the technique for manufacturing bumps (A) and the technique for manufacturing bumps (B), bump electrodes having a low melting point composition, specifically bump electrodes having a composition comprising 37% by weight of Pb (lead) and 63% by weight of Sn (tin), can be easily manufactured, in comparison to a technique for manufacturing bumps comprising forming bump electrodes using a vapor deposition method. Furthermore, because the amount of the solder paste material can be increased by changing the thickness of the screen mask and the area of the openings, bump electrodes having a large height, specifically bump electrodes having a height of 40 xcexcm or more, can be easily manufactured, in comparison to a technique for manufacturing bumps comprising forming bump electrodes using a plating method. Furthermore, because bump electrodes can be formed at once on the surfaces of the plural electrode pads formed on one surface of the substrate, the cost of manufacturing bump electrodes can be reduced, in comparison to a technique for manufacturing bumps comprising forming bump electrodes using a ball bonding method. Furthermore, because bump electrodes are formed by melting the solder paste material formed on the surfaces of the plural electrode pads, respective bump electrodes can be certainly reliably formed on the plural electrode pads, in comparison to a technique for manufacturing bumps comprising forming bump electrodes using a ball supplying method. In the ball supplying method, because solder balls previously formed are supplied to the surfaces of the electrode pads with a suction jig, supply shortage is liable to occur.
The technique for manufacturing bumps comprising forming bump electrodes using a vapor deposition method is described, for example, in Japanese Patent Laid-Open No. 275628/1994.
Furthermore, the technique for manufacturing bumps comprising forming bump electrodes using a plating method is described, for example, in Mitsumasa Muraishi et al, xe2x80x9cA Study of High Density High Temperature Solder Bumpxe2x80x9d, Materials for 1994 Autumn Meeting of The Institute of Electronics, Information and Communication Engineers, p. 28.
Furthermore, the technique for manufacturing bumps comprising forming bump electrodes using a ball bonding method is described, for example, in Mishina et al, xe2x80x9cMicrobump Formation Technologyxe2x80x9d, Materials for Seminars on Practical Application of Fine Pitch SMT on November of 1996, p. 6-1 to 11.
Furthermore, the technique for manufacturing bumps comprising forming bump electrodes using a ball supplying method is described, for example, in Japanese Patent Laid-Open No. 129374/1993.
In the technique for manufacturing bumps comprising forming bump electrodes using a solder paste material, the size of the bump electrodes can be freely set by measuring the amount of the solder paste material formed on the electrode pads of the substrate with the thickness of the screen mask and the area of the openings. However, in the invention, the following problems have been found as a result of investigations of the technique for manufacturing bumps.
(1) In the technique for manufacturing bumps (A), because the screen mask is removed from the flat plate along with the solder paste material filled in the openings of the screen mask, a part of the solder paste material filled in the openings of the screen mask is left on the flat plate upon removing the screen mask from the flat plate. Accordingly, the amount of the solder paste material in the openings of the screen mask removed from the flat plate fluctuates, and thus the size of the bump electrodes becomes non-uniform. In the case where the size of the bump electrodes becomes non-uniform, the height of the bump electrodes fluctuates, and when, for example, a semiconductor chip is mounted on a circuit board through plural bump electrodes, connection failure occurs, in which the electrode pad of the circuit board is not electrically connected to the electrode pad of the semiconductor chip.
Furthermore, in the technique for manufacturing bumps (A), because the screen mask is fitted to the flat plate, and then the solder paste material is filled in the openings of the screen mask with a squeegee, the solder paste material leaks between the screen mask and the flat plate from the openings of the screen mask upon filling the solder paste material in the openings of the screen mask, and thus excessive solder paste material is attached on the fitted surface of the screen mask removed-from the flat plate. The excessive solder paste material is transferred to spaces among the electrode pads of the substrate upon fitting the screen mask to the substrate. Therefore, when the solder paste material filled in the openings of the screen mask is melted to form bump electrodes, an electrically conductive foreign matter is formed among the electrode pads of the substrate from the excessive solder paste material, and thus a short circuit is formed among the electrode pads of the substrate (a semiconductor chip or a circuit board). The short circuit among the electrode pads of the substrate becomes significant when the interval of the arrangement of the electrode pads is narrow.
(2) In the technique for manufacturing bumps (B), because the screen mask is removed from the substrate in such a manner that the solder paste material filled in the openings of the screen mask remains on the electrode pads of the substrate, a part of the solder paste material is left in the openings of the screen mask upon removing the screen mask from the substrate. Therefore, the amount of the solder paste material remaining on the electrode pads of the substrate fluctuates, and thus the size of the bump electrodes becomes non-uniform as similar to the technique for manufacturing bumps (A).
Furthermore, in the technique for manufacturing bumps (B), because the screen mask is fitted to the substrate, and then the solder paste material is filled in the openings of the screen mask with a squeegee, the solder paste material leaks between the screen mask and the substrate from the openings of the screen mask upon filling the solder paste material in the openings of the screen mask, and thus excessive solder paste material remains among and between the electrode pads of the substrate. Therefore, when the solder paste material formed on the electrode pads of the substrate is melted to form bump electrodes, an electrically conductive foreign matter is formed among and between the electrode pads of the substrate from the excessive solder paste material, and thus a short circuit is formed among the electrode pads of the substrate (a semiconductor chip or a circuit board), as similar to the technique for manufacturing bumps (A).
An object of the invention is to provide a technique in that size of bump electrodes formed on electrode pads can be uniform.
Another object of the invention is to provide a technique in that a short circuit among electrode pads of a substrate (a semiconductor chip or a circuit board) can be prevented.
The above-described and other objects and novel features of the invention will be apparent from the description of the present specification and the attached drawings.
The summary of the representative embodiment of the inventions disclosed in the present application will be briefly described as follows:
In a method of manufacturing bump electrodes, a solder paste material is filled in concave parts formed on one surface of a jig for forming bumps, and the solder paste material is melted under the condition in that the concave parts of the jig for forming bumps face electrode pads provided on one surface of a substrate (a semiconductor chip or a circuit board), so as to form bump electrodes on the electrode pads of the substrate. The jig for forming bumps is made of a material having a poor wettability with the solder paste material, and the electrode pads are made of a material having a good wettability with the solder paste material. A plurality of the concave parts of the jig for forming bumps are formed in the form of a matrix.
According to the means described above, because the solder paste material filled in the concave parts of the jig for forming bumps is melted to form bump electrodes on the electrode pads of the substrate, the amount of the solder paste material can be constant, and the size of the bump electrodes formed on the electrode pads of the substrate can be uniform.
Furthermore, because the solder paste material filled in the concave parts of the jig for forming bumps does not leak between the jig for forming bumps and the substrate, an electrically conductive foreign matter formed from the leaking excessive solder paste material can be eliminated, and a short circuit among the electrode pads of the substrate can be prevented.